Windows: PowerToys. First thing I get approval to install on a work machine. PowerToys Run (Launchy on roids) saves me from the built in Windows search, a quick calculator, etc. PowerRename gets used more frequently than I care to admit. Video Conference mute is a second nature key combination. Can't remember the name of the window manager module but it is a key part of my workflow.

Android: As I've mentioned in a reply, Edge Gestures has been on my phone for years (first installed on a Pixel 3). Having 10+ apps accessible (especially 2FA, password vault, home assistant) from any screen, plus gestures for quick controls (flashlight, brightness slider) is incredibly handy. And unlike the notification shade, the edges of the phone can actually be reached with your thumb.

Linux: Docker. It's been an instrumental part of building out my home server which allowed me to kill my Microsoft 365 & Google One subscriptions. For me it has been the gateway drug in to learning more and more about self hosting - to Proxmox, LXCs & VMs, pihole and unbound, etc.